Imaging is possible based on tomographic reconstruction techniques such as computed tomography, although ultrasonic pulse echo imaging is based on focusing techniques. It is possible to obtain three-dimensional imaging data by the tomographic method. When divergent waves are insonified toward a target by a part of a spherical surface, backscattered waves which are generated at the target are received by the transducer, and the echo signal on a delayed time is expressed as the integral of scattered waves at the surface of the radius proportional to the delay. If the transducer has both convex and concave parts of the spherical surface, both divergent waves and convergent waves can be generated. These waves are focused onto the arc on the spherical surface; thus the amplitude at the delay of the received echoes is expressed as the product of the backscatter coefficient on the arc and the diffraction term. Those values are equivalent to the projection data as the tomographic reconstruction technique. Therefore the distributions of the backscatter coefficient on the spherical surface are reconstructed from the projection of the echoes. In this study the effects of the angle dependency of the amplitude on the spherical surface due to the diffraction term are discussed and then the method for correction is described.